1. Field of the Invention
The present invention relates to a permanent magnet reluctance motor wherein a plurality of permanent magnets are provided in combination.
2. Description of the Related Art
A permanent magnet reluctance motor according to previous applications by the present applicants (Japanese Patent Application Number H. 11-043869 and Japanese Patent Application Number H. 11-122000) is of the construction shown in radial cross-section in FIG. 1. In FIG. 1, a stator 1 is provided with an armature coil 2, within which a rotor 3 is provided.
Rotor 3 is provided with a rotor core 4 and permanent magnet 6. In rotor core 4 there are formed a direction where magnetization is easy and a direction where magnetization is difficult. Specifically, in order to form magnetic irregularities, rotor core 4 is constructed by laminating electromagnetic steel plates provided with eight permanent magnet embedding holes 5 in which are embedded permanent magnets 6 along the direction of easy magnetization. The eight permanent magnet embedding holes 5 form four projecting poles by being arranged in a xe2x80x9c+xe2x80x9d arrangement. That is, the regions sandwiched by permanent magnet embedding holes 5 which are positioned on both sides of non-magnetic portions 8 represent between-pole portions 4b constituting xe2x80x9cconcavitiesxe2x80x9d in terms of magnetic polarity. Furthermore, permanent magnets 6 which are magnetized so as to cancel the magnetic flux of the armature current passing through adjacent between-pole portions 4b are arranged in permanent magnet embedding holes 5. That is, the relationship of the permanent magnets 6 which are on both sides of pole region 4a is that their directions of magnetization are the same, while the relationship of the two permanent magnets 6 which are positioned on both sides of between-pole region 4b is that their directions of magnetization are mutually opposite in the circumferential direction of rotor 3. Permanent magnets 6 are preferably magnetized practically in the circumferential direction and even more preferably in a direction practically perpendicular to the axis of the magnetic poles.
Next, the operation of the permanent magnet reluctance motor according to the previous application described above will be described. FIG. 2 shows the magnetic flux "PHgr"d of the component in the direction along the axis of the magnetic pole of rotor core 4 produced by the armature current of the d axis; in order that the core of pole region 4a should provide a magnetic path, the magnetic construction is such that magnetic flux can easily flow, the magnetic resistance in the magnetic path in this direction being very small. Reference symbol 8 denotes a non-magnetic region.
FIG. 3 shows the magnetic flux "PHgr"q created by the armature current of the q axis of the component in the direction along the axis joining the center of between-pole region 4b and the center of rotor 3. Magnetic flux "PHgr"q of this between-pole region 4b forms a magnetic path of non-magnetic region 8 and between-pole region 4b that runs transversely across permanent magnets 6. Since the relative permeability of non-magnetic region 8 is xe2x80x9c1xe2x80x9d and the relative permeability of permanent magnets 6 is also practically xe2x80x9c1xe2x80x9d, the magnetic flux "PHgr"q produced by the armature current is lowered by the high magnetic resistance action.
The permanent magnets 6 between the magnetic poles are magnetized in the direction practically perpendicular to the axis of the magnetic pole so that, as shown in FIG. 4, a magnetic circuit "PHgr"ma is formed whereby the magnetic flux generated by permanent magnet 6 flows in the circumferential direction of magnetic region 7 at the boundary of the circumference of the rotor core, through pole region 4a, returning to the pole of opposite polarity.
Also, some of the flux of the permanent magnet 6 passes through the gap, through the pole region 4a of rotor 3 or permanent magnets 6 of the adjacent pole, returning to the original permanent magnets 6 and thereby also forming a magnetic circuit "PHgr"mb.
As shown in FIG. 3, the interlinking magnetic flux of these permanent magnets 6 is distributed in the opposite direction to the magnetic flux "PHgr"q of the component in the direction of the between-pole center axis produced by the armature current of the q axis, and repels and cancels ingress of armature flux "PHgr"q from the between-pole region 4b. In the gap outside between-pole region 4b, the gap magnetic flux density created by the armature current is lowered by the magnetic flux of permanent magnets 6, causing it to show larger variation than the gap magnetic flux density outside pole region 4a. That is, the variation of the gap magnetic flux density with respect to position of rotor 3 becomes large, resulting in a large variation of magnetic energy. Furthermore, under load, at the boundary of pole region 4a and between-pole region 4b, a magnetic region 7 exists where there is magnetic short-circuiting; this is strongly magnetically saturated by the load current. As a result, the magnetic flux of permanent magnets 6 that is distributed between the poles is increased. Irregularities representing large changes in the gap flux density distribution are therefore created due to the magnetic flux of permanent magnets 6 and the high magnetic resistance of non-magnetic region 8 and permanent magnets 6; considerable changes in magnetic energy are thereby produced, as a result of which large output is obtained.
The following effects are manifested in regard to the adjustment width of terminal voltage in order to obtain variable speed operation over a wide range. With this proposed permanent magnet reluctance motor, since permanent magnets 6 were only provided over part of the concave portion of the between-pole region 4b, the surface area of permanent magnets 6 was more restricted than in the case of an ordinary permanent magnet motor in which permanent magnets 6 are provided over practically the entire circumference of the surface of rotor 3 and, as a result, the amount of interlinking magnetic flux produced by the permanent magnets 6 was small.
Furthermore, in the non-excited condition, practically all of the magnetic flux of permanent magnets 6 was leakage magnetic flux within rotor core 4 passing through magnetic region 7 of the magnetic pole boundary region. Consequently, since, in this condition, the induced voltage can be made very small, core loss in the non-excited condition is small. Also, overcurrent is small even when armature coil 2 is in a short-circuited defective condition.
When loaded, terminal voltage is induced by addition of the interlinking magnetic flux created by the armature current (exciting current component and torque current component of the reluctance motor) to the interlinking magnetic flux created by the permanent magnets 6.
In an ordinary permanent magnet reluctance, the interlinkage magnetic flux of the permanent magnets 6 represents practically all of the terminal voltage, so it is difficult to adjust the terminal voltage; however, in this permanent magnet reluctance motor, the interlinkage magnetic flux of permanent magnets 6 is small, so a large width of adjustment of the terminal voltage can be achieved by providing a large adjustment of the exciting current component. That is, since the exciting current component can be adjusted in accordance with speed so that the voltage is below the power source voltage, wide-range variable speed operation can be achieved with fixed voltage from the base speed. Also, since the voltage is not suppressed, since a weak field system is implemented under forcible control, even if control becomes inoperable when rotating at high speed, no overvoltage can be generated.
Furthermore, since permanent magnets 6 are also embedded within the core, rotor core 4 constitutes a retaining mechanism for permanent magnets 6, preventing permanent magnets 6 from being flung outwards by the rotation.
As shown in FIG. 3, in a permanent magnet reluctance motor constructed as above, since the magnetic flux xe2x80x9c"PHgr"qxe2x80x9d produced by the q axis current in the direction of the concavities of rotor 3 produced by the armature current flows through the circumferential-side thin-wall region 18 of the permanent magnet embedding holes and through the thin-wall bridge region 19 on the side nearest the center between the magnetic poles, the difference of the magnetic flux xe2x80x9c"PHgr"qxe2x80x9d produced by the d axis current and the magnetic flux xe2x80x9c"PHgr"qxe2x80x9d produced by the q axis current is small, decreasing the reluctance torque. It may be thought that these should be made as narrow as possible in the radial direction in order to decrease the reactive magnetic flux flowing through the circumferential-side thin-wall region 18 of the permanent magnet embedding holes 5 from the circumferential-side of the non-magnetic region 8, i.e. the magnetic flux xe2x80x9c"PHgr"qxe2x80x9d produced by the reactive q axis current in regard to the rotary torque, and, as shown in FIG. 5, in order to decrease the leakage of magnetic flux generated from permanent magnets 6 (i.e. the reactive magnetic flux 17 of the permanent magnets) in the vicinity of the permanent magnet embedding holes 5 of rotor core 4 and on the circumferential side of between-pole regions 4b. However, with such a shape, it is difficult to support the centrifugal force of the permanent magnets 6 and in particular when applied to an high-speed motor there was a risk of permanent magnets 6 being flung out, causing damage to the rotor 3.
Furthermore, in order to secure the active magnetic flux that is necessary for performance, it is necessary to increase the quantity of permanent magnets 6 in order to compensate for the quantity of magnetic flux corresponding to reactive magnetic flux and leakage magnetic flux, but, because of spatial problems in regard to the overall volume of rotor 3 and strength problems involved in further increasing the force produced by the centrifugal force of the permanent magnets 6, it is difficult to simply increase the quantity of permanent magnets 6.
Also, in order to reduce stress concentrations, in permanent magnet embedding holes 5, the corners of the holes are made of arcuate shape (circular arc); however, since gaps are produced between both sides of the permanent magnets 6 and the permanent magnet embedding holes 5, wedges 15 are necessary in order to locate permanent magnets 6 in position. Consequently, in this construction, permanent magnets 6 must be positionally located by a plurality of wedges 15, increasing the amount of work involved in manufacture and raising costs; furthermore, if the adhesive used to fix permanent magnets 6 and position-locating wedges 15 deteriorated resulting in loss of adhesive effect, the position-locating wedges 15 or permanent magnets 6 could directly strike the circumferential-side thin-wall regions 18 of permanent magnet embedding holes 5 from one side, so stress concentration occurred since these were of small thickness; thus cases occurred of the permanent magnets 6 being flung out or damage to rotor 3 being produced, making the motor incapable of use.
Furthermore, although stress concentration could be correspondingly reduced by increasing the bending radius (radius of curvature) of the corners and both ends of the permanent magnet embedding holes 5, with a construction as above, the shape of wedges 15 for locating permanent magnets 6 in position was made more complicated so it was not possible to increase the bending radius by more than the thickness of permanent magnets 6, with the result that, when speed of rotation and output were further raised, increased force created by the centrifugal force of the permanent magnets 6 made it difficult to support the centrifugal force of permanent magnets 6, with a risk of permanent magnets 6 being flung outwards, damaging rotor 3.
Accordingly, one object of the present invention is to provide a novel permanent magnet reluctance motor wherein the wedges for positional location of the permanent magnets are dispensed with and insertion of the permanent magnets in assembly is facilitated, thereby making it possible to mechanize the task of magnet insertion during manufacture and wherein, even when the adhesive used co fix the permanent magnets has deteriorated, there is no risk of the permanent magnets being flung out or rotation being impaired and wherein high output, high efficiency, high-speed rotation, reliability and improved ease of manufacture can be achieved by optimizing the cross-sectional shape of the rotor.
In order to achieve the above object, the present invention is constructed as follows. Specifically, in a permanent magnet reluctance motor comprising: a stator having an armature coil and a rotor providing magnetic irregularities in the circumferential direction by the provision of permanent magnets in permanent magnet embedding holes within the rotor core such as to cancel the magnetic flux of the armature passing through between adjacent magnetic poles and by the provision of non-magnetic regions on the circumferential-side of the permanent magnets between the magnetic poles; projections are provided for positional location of the permanent magnets in such a way as to project into the permanent magnet embedding holes within the core of the rotor.